I really like the Redfield Revolution 3-9x, but I like my 4-12x even more. My 4-12x is mounted on a .17 HMR, I have knocked squirrels out of trees 120 yards into the woods with it. Overall great clarity and light transmission. Nothing but positive things to say about them.

Hunting around here, we don't have massive open spaces so for me the Nikon BDC reticle has a lot of dots that wouldn't be used for much. Most of our shots target or otherwise is going to be 100-150 yards so The Accu-Range reticle works very well, I have to take very little account of drop, put the circle and cross-hairs on target and squeeze one off.

If you have more open space where you are shooting your .308 enough to need holdover you may be able to get more long range accuracy out of the Nikon prostaff.

Medium height rings will most likely accommodate a 40mm objective. Leupold is a good choice of scope rings.